The overarching theme of Project 1 (Integration) is integration, with the following objectives: (a) to continue research on the classification and identification of children with learning disabilities (LDs) using statistical simulation and real data (b) to extend this work to English learners (Els), and (c) to expand the use of meta- analysis and extend previous syntheses to co-morbid disabilities and to Els. The activities integrate research across projects, approaches, frameworks, settings, and populations. With this overarching purpose of Integration and these stated objectives, Project 1 has three specific aims. Specific Aim 1 (Classification and Identification) addresses the challenges inherent in the identification and classification of LDs, targeting a historical mismatch permeating the literature between approach (dimensional) and framework (categorical). Project 1 seeks to investigate the inherent nature of LDs as either dimensional or non-dimensional while moving beyond current approaches to identification to develop and evaluate new approaches that overcome the known problems with existing approaches. Aim 1 draws on simulated data and actual data from Projects 2- 4 in the prior and current awards, and Projects 1 (Classification) and 3 (Remediation) from the first award. New methods include (a) latent variable models appropriate for categorical and dimensional frameworks, and (b) a reframing of RTI in terms of expected magnitude of response to instruction, consistent with a dimensional view of LDs. We expect to find support for our reconceptualization of RTI in terms of expected magnitude of response that is consistent with ideas from personalized medicine as applied to student learning and instruction. In addition, application of these methods to a large sample of Els will address fundamental questions of how to identify LDs in Els with persistent academic difficulties. Specific Aim 2 (External Validity of Identification Methods) addresses the validity of the identification and classification methods developed and tested under Aim 1. Using data collected under Projects 2 (Attention), 4 (Neuroimaging), and 5 (Epigenetics), we will compare children from Project 3 (Intervention) identified using different methods under Aim 1 on measures of attention, written expression, math, and other domains, including measures of neural response and epigenetics. We will also work with Project 4 (Neuroimaging) to develop a measure of neural specificity to use in external validation of identifications and to characterize RTI. Specific Aim 3 (Synthesis) continues and expands our work on empirical synthesis from the previous five years. We propose to undertake meta-analytic work addressing (a) the history of LD identification drawing on our prior 100 year review (Scammacca, et al., 2016), (b) predictors of intervention response in comorbid disabilities; (c) cognitive similarities and differences between comorbid and singular disabilities, including multiple academic domains with and without ADD/ADHD; (d) expand previous meta-analyses on identification to synthesize the literature on identification of disabilities in children who are Els; and (e) to update the Grigorenko (2005) synthesis of the LD-genetics literature.